From 732f7b079667644e1ea65af77ebd79aa34a322f4 Mon Sep 17 00:00:00 2001
From: LordBaryhobal <lordbaryhobal@gmail.com>
Date: Tue, 16 Jun 2026 14:02:45 +0200
Subject: [PATCH] feat(checker): add environment preamble

this adds some builtin functions such as the builtin type constructors
---
 midas/checker/preamble.py | 121 ++++++++++++++++++++++++++++++++++++++
 midas/checker/python.py   |   3 +-
 midas/checker/types.py    |   8 +--
 3 files changed, 127 insertions(+), 5 deletions(-)
 create mode 100644 midas/checker/preamble.py

diff --git a/midas/checker/preamble.py b/midas/checker/preamble.py
new file mode 100644
index 0000000..a543dd9
--- /dev/null
+++ b/midas/checker/preamble.py
@@ -0,0 +1,121 @@
+from dataclasses import dataclass
+
+from midas.checker.environment import Environment
+from midas.checker.registry import TypesRegistry
+from midas.checker.types import Function, GenericType, TopType, Type, TypeVar, UnitType
+
+
+@dataclass(frozen=True)
+class Param:
+    name: str
+    type: Type
+    required: bool = True
+
+
+class Preamble(Environment):
+    def __init__(self, types: TypesRegistry) -> None:
+        super().__init__()
+        self._types: TypesRegistry = types
+
+        self._def_type_constructor("object")
+        self._def_type_constructor("float")
+        self._def_type_constructor("int")
+        self._def_type_constructor("bool")
+        self._def_type_constructor("str")
+        self._def_function(
+            name="list",
+            pos=[Param("object", TopType())],
+            returns=self._list_of(TopType()),
+        )
+
+        # TODO: use sink
+        self._def_function(
+            name="print",
+            pos=[Param("object", TopType())],
+            returns=UnitType(),
+        )
+
+        map_in = TypeVar(name="T", bound=None)
+        map_out = TypeVar(name="U", bound=None)
+        mapper = self._make_function(
+            name="MapTransform",
+            pos=[Param("v", map_in)],
+            returns=map_out,
+        )
+        self._def_function(
+            name="map",
+            pos=[
+                Param("transform", mapper),
+                Param(
+                    "iterable",
+                    self._list_of(map_in),  # TODO: replace with Iterable[T]
+                ),
+            ],
+            returns=self._list_of(map_out),  # TODO: replace with Iterable[U]
+        )
+
+    def _list_of(self, item_type: Type) -> Type:
+        return self._types.apply_generic(self._types.get_type("list"), [item_type])
+
+    def _def_type_constructor(self, name: str):
+        # TODO: more specific arg types
+        self._def_function(
+            name=name,
+            pos=[Param("object", TopType())],
+            returns=self._types.get_type(name),
+        )
+
+    def _make_function(
+        self,
+        *,
+        name: str,
+        pos: list[Param] = [],
+        mixed: list[Param] = [],
+        kw: list[Param] = [],
+        returns: Type = UnitType(),
+        type_vars: list[TypeVar] = [],
+    ) -> Type:
+        def map_args(params: list[Param], offset: int) -> list[Function.Argument]:
+            return [
+                Function.Argument(
+                    pos=i + offset,
+                    name=param.name,
+                    type=param.type,
+                    required=param.required,
+                )
+                for i, param in enumerate(params)
+            ]
+
+        function = Function(
+            pos_args=map_args(pos, 0),
+            args=map_args(mixed, len(pos)),
+            kw_args=map_args(kw, len(pos) + len(mixed)),
+            returns=returns,
+        )
+        if len(type_vars) != 0:
+            function = GenericType(
+                name=name,
+                params=type_vars,
+                body=function,
+            )
+        return function
+
+    def _def_function(
+        self,
+        *,
+        name: str,
+        pos: list[Param] = [],
+        mixed: list[Param] = [],
+        kw: list[Param] = [],
+        returns: Type = UnitType(),
+        type_vars: list[TypeVar] = [],
+    ):
+        function: Type = self._make_function(
+            name=name,
+            pos=pos,
+            mixed=mixed,
+            kw=kw,
+            returns=returns,
+            type_vars=type_vars,
+        )
+        self.define(name, function)
diff --git a/midas/checker/python.py b/midas/checker/python.py
index b4da4ba..6e6ea1a 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -7,6 +7,7 @@ import midas.ast.python as p
 from midas.ast.location import Location
 from midas.checker.environment import Environment
 from midas.checker.operators import COMPARATOR_METHODS, OPERATOR_METHODS, UNARY_METHODS
+from midas.checker.preamble import Preamble
 from midas.checker.registry import TypesRegistry
 from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.resolver import Resolver
@@ -56,7 +57,7 @@ class PythonTyper(
         self.logger: logging.Logger = logging.getLogger("PythonTyper")
         self.reporter: FileReporter = reporter.for_file(None)
         self.types: TypesRegistry = types
-        self.global_env: Environment = Environment()
+        self.global_env: Environment = Preamble(self.types)
         self.env: Environment = self.global_env
         self.locals: dict[p.Expr, int] = {}
         self.judgements: list[tuple[p.Expr, Type]] = []
diff --git a/midas/checker/types.py b/midas/checker/types.py
index c6d41d1..f2fef3b 100644
--- a/midas/checker/types.py
+++ b/midas/checker/types.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import Optional
 
 
@@ -41,9 +41,9 @@ class UnitType:
 
 @dataclass(frozen=True, kw_only=True)
 class Function:
-    pos_args: list[Argument]
-    args: list[Argument]
-    kw_args: list[Argument]
+    pos_args: list[Argument] = field(default_factory=list)
+    args: list[Argument] = field(default_factory=list)
+    kw_args: list[Argument] = field(default_factory=list)
     returns: Type
 
     def __str__(self) -> str: